Percentage power control apparatus



Ma 31, 1949; j

R. s. DAVIES PERCENTAGE POWER CONTROL APPARATUS Filed April 5, 1944 FlGLi Z A 1 [HIE/l6 F IG.3 '17 I 22 NON-LINEHE Q}! F164 INVENTOR.

63 I RICHARDSTILLMAN DAVIES /64 VOLTAGE.

ATTORNE Y Patented May 31, 1949 PERCENTAGE POWER CONTROL APPARATUS Richard Stillman Davies, Philadelphia, Pa., as-

signor to The Budd Company, Philadelphia, Pa.,

a corporation of Penns ylvania Application April 5, 1944, Serial No. 529,621

22 Claims.

This invention relates to control apparatus and circuits associated therewith for activating a power circuit after a predetermined percentage change in the voltage as applied to the power circuit.

the metal sections.

tion.

more briefly, a percentage apparatus.

In various power circuits subject to voltage which functions on a change of resistance or on changes, it is often found desirable that when the a change of voltage, if the current be constant, at voltages change a predetermined percentage of a specified load point. the original or main voltage of the power cir- Accordingly, an object of the present invention cuit, mechanism be set in action to open the is to provide means for de-energizing a, circuit on power circuit. One instance of such a power the occurrence of a predetermined change in the circuit is that used in resistance welding where voltage of a primarycircuit. Another object of voltage is applied at the electrodes of a welding this invention is to provide such a circuit artransformer secondary in order to produce a weld rangement which is operable when the change in by fusion of the metal at the interface of the the voltage is a fixed percentage of the same, contacting metals forming the workpiece whereirrespective of the original value of the voltage. by a solid junction may be obtained between Still another object of the invention is to prop e al es r h ha vide a circuit of the type mentioned which may revealed the fact that a large proportion of the be adapted for actuation upon a non-rectilinear resistance of the workpiece in resistance welding percentage change of the power unit voltage or is at the surface area between the contacting a component thereof. Further objects pertainmetal sect o s of e wo p a consequently, ing to circuit arrangements are the utilization of as the heating current flows and fusion of the a limited number of elements, which may be e al resu n this e this resistance (1 adapted for operation with relatively limited time creases as the fusion progresses from a central lag and which are operable within limits at difpoint outwardly until the entire interface in the ferent initial voltages as applied to the inlet tercylindrical area defined by the contour of the minals of the circuit. electrode terminals disappears. This disappear- In the accompanying drawings: ance of interface resistance is, of course, accom- Figure 1 illustrates the basic circuit of the panied by a drop in potential which, in metals comparator as applicable to any type electrical such as certain steels, may be as high as 25% power circuit; and, as a rule, averages around 20%. This drop Figure 2 is a circuit diagram illustrating the apis of sufficient value to be utilized in a control plication of the basic circuit of Figure 1 to a or actuating circuit for opening the main power resistance welding system; circuit. Moreover, experiment has revealed that Figure 3 is a detail of a modified form of perthe strength of the weld is directly related to the centage control, and percentage change of resistance at the weld, so Figure 4 is a set of curves illustrating the that if the percentage means he set at a selected percentage changes of circuit when incorporating value corresponding to a certain weld strength the device of Figure 3. value, the indicating or control circuit will not Referring to Figure 1, the numerals I0 and II function until this percentage change has 00- indicate input terminals fromapower source, and curred. Consequently, if control apparatus, such the numerals l2 and I3 refer to terminals in load as hereinabove referred to, is employed in concircuits controlled by the actuating apparatus and nection with the drop in potential or resistance at circuits of the invention. the d point, the P y Welding r t may From the terminals l0 and II, the main switch be opened as soon as the weld is completed or M passes current to a resistor l5 which lies appropriate indication be made of weld compleacross the maximum potential points of the terminals. The voltage as applied to the terminals Various means may be employed to accomplish I 0 and II is direct and, consequently, the rethe energization of a power opening device, but sistor has a positive terminal l6 and a negain the present invention I utilize what may be tive terminal l1. Adjacent the resistor 15 are two referred to as a percentage control apparatus or, gas tetrodes I8 and Is.

That is tube [8 is connected to the negative terminal l1 an arrangement of circuit means for establishof the resistor l5, and the screen grid 2| of tube ins a potential fixed with reference to an average 2 main voltage applied to the power unit and usable in conjunction with a change of voltage from the main voltage to the fixed voltage to activate the power unit circuit. Alternatively stated, the invention pertains to a circuit having power means The screen grid 20 of I9 is connected to a slider contact 22 movable on the resistor l so as to secure by its movement any desired percentage of voltage drop between the points It and IT, applicable to the screen grid 2!. It is evident, therefore, that the screen grid of tube i8 is always at a lower potential than that of the screen grid 2| of tube 19. Anode 23 of tube 8,; is. connected to the, positive terminal 25 of a so ice of plate potential through a relay coil 26. Similarly, anode 21 of tube i9 is connected to the positive terminal 25 of the plate potential source through a relay coil 28. The relay coil 26 is operative tomove contact plates 29 into and out of engagement with contacts 30 in the power actuating circuit; relay 2 3; is operative to actuate contact plate 3| with reference to contacts 32 and 33 in the percentage circuit, the relationship of said contacts being more fully described hereinafter. The negative terminal 34; of the plate potential source is connected through a manual switch 35 to the positive terminal it of the resistor i5, as well as; to the cathode 36 qt t ta -g, nd cathode til; or tube is so that a circuit is co: pleted iron-1 the potential source 25, lid through each, ofi'the tetrodes which is operable,on proper"condition'ng of the controller gridsv of? the tubes jto'ac "vate the relays 26 and 28 and to close the power circuits including terminslsI "T2 1. 9 1 '5' ontr l id 48: i. t bs oi ube. 9 r co nec l arate source oi constant. I nals ill and M, the. control grid connection being directly to the po ve. terminal Ml of this potential source' Conn cted, across this potential source, also, is a poten a1 divider 42 having resistors iil and 4A. some ted in series. At an intermediate point 45 between these two resistors 83,3 and 44, connection'i made both through a resistor 45 to relay-contact 3,2 of relay '28 and h u capac t '4 relay. Alsoff'rjom, this point, connection i made t the. ath u jne r a vacuum, triode as. Anode lill;v ofthis tuloe-is connected' directly to the conductor 5}. connecting the, terminal l6 of the resistor t5: nd switch. 3,5.The grid 5; of tuloe 4a is connected direc tly'to the relayv contact 33. The grid current of the-t :be,.4, 9 ,is normally small.

Additional elements, of the, percentage circuit include the maniial switchl normally forming a closed conducting pathfro'm the negative terminalresistor; 4i; and. therelay. contact 33 and the res filiqr iil con ectedh etween the conductor 5| and thepositive terminal, of potential divider resistor 43.,

In employing the basic circuit of the percentage apparatus, as, above, described, the same is insentedlbetweenfthe source, at terminals Ill and H and the switch means leading from terminals l zla-an d direct current voltage is applied to thesources 4Q, 41 and 2 5, '34, The main op erating switch M, is then closed, the same being ganged with. 'losedv switch. 53'and open switch 35"to bring "about simultaneously an opening of switch 5.3, and a closure. of switch 35 The a QO i ectiQn'bet ieQn i ll %l W FQ and 5 3, is sh-ownioyv a dashed, line, the arrows indicat ing. the, simultaneous, movement of the switches on. closure, or main switghi It, A reversed movementl would, re uire a reversal, of all arrows,

Sub$quent to, the.v conneqtion of potential source A fi -4,1, and. prior.fto the closure of the wi SW .9 s ur nt l ws h oug h tential. divider. 4.2 and, also, through, the resistor 4E o hat a; fixed potential difference is applied to the capacitor il, ith the positive side as t8 and control, grid 39 together and to a seppotential having termito contact 33 of the same through tube 49.

indicated. As a consequence of this potential difference on the capacitor 41, a substantially negative potential is applied to the grid 52 of the tube 4?! so that the current flow through this tube is negligible. However, on the opening of switch 53, with the closure of the main switch I4 capacitor 41; discharges through the normally closed contact plate 4| thereby reducing the bias of grid 52 and increasing the flow of current The result of this action is the control grids 38 the potential of with to n eas and 39 of tubes 18- and I9, respectively,

, reference to the potentials of cathodes 36 and 31 and when a predetermined voltage is reached, which is related to the voltage impressed on the screen grid 2!, the tube l9 strikes and the relay 28 is immediately energized to open contacts 32, It, is. at once apparent that as soon as these contacts are opened, the discharge of the capacitor 41. ceases and, hence, the potential of grid 52 of tube, 49 is fixed. It, is also apparent that the steps as described in the operation take placev over a short interval. of t'me, so that practically as soon as the switch I4 is closed the standard or comparison voltage established in the tetrode [8 has afixedvalue.

Further action of. the, percentage apparatus will depend upon the original voltage as applied to there-sister l5. If thetoriginal voltage is maintained without change, there will be no energiation oi therelay 26,130 close the actuating circuit. Should, however, the voltage across the resistor L5. diminish by a percentage determined by. the setting of the slider 22 of the resistor l5, at this point. the screen grid 20 and control grid as of tube l8 are at the striking point at which tube 19 previously was made effective. Consequently, tube, is begins to, transmit currentfreay 26 is energi ed d contacts. are actuated.

It is pointed out that the operation of the ercentage apparatus as above described is in dependent of the absolute, value of thepotential across points l6, H, and of resistor liwithin certain limits as may he contrqlled in the design or. t e ime h ra te st c nd h relays and other apparatus, In actual use, a substantial deviation from, an average valueiof potential be tween points It and Ill Ihay be madeQand for any given value of this range the percentage variation is linear, inasmuch as the resistance per unit length of, the resistor 15' is presumed to be un rm a While, as above indicated, it isdesirable that the controlling means operate on a predetermined fi-xed-peroentage o f the original voltage as applied to the resistor l5 under other conditlOllS Of use, it may be important that there be a variation in the percentage relationship in accordance with the absolute value of the original voltage. For example, in resistance welding when the voltage applied to the electrode terminals is relatively low, it may be desirable to increase the percentage of main voltage efiective on the controlling means while decreasing the percentage as the main voltage increases. Several means may be employed toaccornplishthis result.

One mode of-accomplishing the result is illustrated in Figure 3 wherein for the single resistor I5, is substituted the two series-resistors 60 and BI; Resistor 60 is a linear resist'or bf the usual type, but resistor 6| has non-linear characteristics, consisting ofa material such as silicon carbide, commercially known as Thyrite, or an iron fil mentin a highly heat conductive; atmosphere, such as helium, commercially known asAmperite,

.By connecting these resistors as shown in Figure 3, an increase in the initial voltage I--I 1 will result in a decrease in the value of the resistance in resistor 6|, thus progressively decreasing the percentage value of point 22 in relation to increase of voltage I6I'I. Curve 63 in Figure 4 illustrates this percentage variation, the curve being plotted with a percentage of total voltage ordinate and a total voltage abscissa.

By reversing the series position of resistors 60 and GI a reversal of the voltage-percentage curve as shown by dotted lines 64 will result.

Variation of the curve form of Figure 4 may be obtained by moving slider 22 on resistor 60 or 6|. Also for certain applications, instead of the resistor 6| a vacuum triode may be used. In this use, the resistor 60 remains connected to point I! and the tube is connected in series to point I6, with the plate directly connecting this point. The grid is connected to point I7. Obviously, the tube anode should be operated on the fiat section of the volt-current curve.

In-Figure 2 of the drawing I have shown the basic circuit of Figure 1 adapted for use specifically in relation to a resistance spot welding power unit with certain modifications, which will now be described. The numeral refers to the welding transformer having a primary II connected to the power source terminals I2 and secondary I3, the terminals of which are connected to electrodes I4 between which electrodes a workpiece I5 having multiple contiguous plates is adapted for insertion. Connected around the workpiece and associated electrodes is the primary 76 of a transformer 77, the ends of the secondary I3 of which are connected to the anodes IQ of rectifying tubes 80. Substantially constant direct current is taken off this rectifying unit by the conductor 8| connected to the mid-point of secondary 18, and conductor 82 connected to the cathodes of each of the rectifying tubes 80, and this direct current is smoothed by the capacitative filter including the capacitors 83 and 34 and the choke coil 85. A voltage drop is secured between the conductors 8| and 82 through the percentage resistor I5, the numeral I6 indicating the positive end and the numeral I! the negative end of said resistor, as in Figure 1. Gas tetrodes 89 and 89, as in the arrangement of Figure 1, are employed, the screen grid 90 of tube 88 having connection to resistor point I! and the screen grid 9| of tube 89 having connection to a slide contact 22 engaging the resistor I5. Movement of the slide 22 secures any desired percentage value for the screen grid 9i at which the striking point of tube 89 may be fixed.

The rest of the circuit of Figure 2 follows that of Figure l in main particulars. In the circuit of anode 92 of tube 98, a resistance drop 93 is employed which is intended to be applicable to the grid and cathode of an amplifying thermionic tube from which, with appropriate multiple amplifying and translating means connection is made to a control actuator on which the amplified voltage is made effective to open the welding circuit at'the completion of the weld, as will be more fully described hereinafter. The voltage source 94 applicable to the voltage divider resistors 95 and 95 corresponds to that of Figure 1. Also, the capacitor 4, tube 91, normally closed manual switch 98, resistor 99 between the tetrode cathodes I00 and the-postive side of voltage source 94 correspond respectively to the voltage divider resistors 43, 44, capacitor 41, manual switch 53, tube 549 and resistor 54 of Figure 1. The voltage source IOI and the manual switch I02 correspond to the voltage source 34 35 and switch 53 of Figure 1, these voltage sources supplying current to the connected tubes 88, 89 and I8, I9, respectively.

In the circuit of the anode 92 of tube 89 designated by the numeral I04 a resistor I05 is inserted of such value as to balance the resistor 93 in the circuit I I 5 from the anode 92 of tube 88.- Circuit I04 includes also the relay coil I06 which is adapted to open, when energized, the normally closed relay switch I01. This switch bridges contacts I08 and I09, the contact I09 having connection to the manual switch 98, the capacitor 4 and the grid I I0 of tube 91, and the contact I08 having connection through the resistor I I I to the positive side of the capacitor 4, to the cathode I I 2 of tube 97, and to the point I IS in the voltage divider between the resistors 95 and 96.

The circuit of Figure 2 differs from the circuit of Figure 1 also by detailing the circuit connections between the voltage element 93 in circuit I I 5 and the circuit breaking means of the primary of the welding transformer I0. Any conventional type of direct current amplifier as indicated at I 20 may be used. This amplified voltage is impressed on a relay coil I2I which when energized is adapted to open a normally closed relay switch I22 in the circuit I23 of the welding primary. This circuit includes also a timer I24 for setting a limiting time period during which energy may be supplied the welding unit and this constitutes an insurance against excessive heating in case the apparatus hereinabove described should fail to function properly. Circuit I23 includes also the initiating relay switch I25 which is normally open but which is adapted to be closed by the energize.- tion of the relay coil I28 in circuit with a source of power 121 and an initiating manual switch I 29.

In operation, dependence is placed upon the fact that when the weld formed by fusion of metals at the interface of the contiguous elements of the workpiece forms, the voltage drops, thus originating a voltage impulse which may be translated through the percentage apparatus to the means for opening the welding circuit. Prior to the completion of the weld and after the initiation of the original voltage between the electrodes, the current is rectified through the rectifying unit and is appropriately filtered and applied as a potential difference between the points I 6 and I 1 of the resistor I5.

Prior to closure of the welding circuit capacitor 4 is charged and after closure of the welding circuit by closing of switch I29, with simultaneous closing of switch I02 and opening of switch 98, capacitor 4 discharges through switch I0! and resistor III, thus raising the potential of the grid I I0 of tube 91 to such a point as to cause the tube 89 to strike, as in the first described arrangement. Current thereupon flows in the anode circuit of tube 89 energizing relay coil I06 and opening switch I01 in the circuit of capacitor 4, interrupting the capacitor discharge and consequently fixing the voltage of the control grid of the tetrode 89 and the current flow therethorugh.

On a subsequent reduction of voltage between points I6 and I I of the percentage resistor I5, tube 88 strikes and the voltage drop developed across resistor 93 is amplified and made effective to energize relay I2I and open the relay switch I22 and thus disrupt the welding circuit. Initiating switch I28 is then opened with simultaneous closure of switch 98 and opening of switch I02. The circuit is thus conditioned for a new welding cycle.

For best results it is pointed, out that in each of the disclosed forms the anode potential on the tetrodes should be substantially equal; and that the capacitors 41, and 6 should have lowleakage values. It is pointed out further that the term "voltage in the specification and claims is used with the assumption that the current value is maintained constant.

It is obvious that the inventive features of the described circuits resides in the combination of elements and in the relationship of the various branch circuits. It is obvious also that while the clrcuit is applied readily to power cut-off on load voltage change, it may actuate any other" desired power mechanism, such as indicating means. Also, whilethe specificdescriptlon has been related to a main voltage in which an actuating voltage drop occurs, the actuation may be made to depend on; a rise in voltage in order to protect sensitive equipment or for other analogous objects. To accomplish this it will be necessary to make small changes in the circuit. For example, in Fig. l the direct current voltage applied to terminals Hi and H should be reversed, the connections to resistor points N and I interchanged, and the tetrode screen grids 20- and 21 be connected directly to point 45- of the voltage divider, in order to, secure actuation on a percentage rise in main voltage.

It is pointed out that while the conventional terms control and screen-"have been used to designate the grids of tubes I 8, i9, 88", 89, such terms, are not intendedto be limiting, the essential characteristic of the. tube and its tube grids being that the tube strikes and transmits power only when each grid attains a predetermined striking potential; hence the mode of connection of the tube grids to thecircuit, is normally a matter onlyof choice within the skill of the technician.

Other variations and modifications coming within the scope of theclaims-may also: bev made.

What is claimed is:

1. In, an electric control system, an electric power unit subject tovoltage change from an initial" voltage, a control element adapted for conmotiontosaid power unit and having a voltage variable with that of" said? unit, percentage means for establishing, as a standard, a voltage at. a fixed percentage of be energized at achange of the initial voltage to said standard. voltage, said standard percentage being constant-for varying values of initial voltage.

2. In an electric controlt'system, electrical power unit subject to a voltage change iromian initial value, a percentage apparatus. for establishing a percentage relationship between the initial voltage as applied to saidunit and a subsequent different voltage, said apparatus comprising a resistor connected across a, direct current component of the initial. voltage of said power unit, afirst gas tetrodehaving a first; grid connected to the negative resistor terminal; a second gas tetrod'e having a first grid connected to said resistor at a point displaced from said negative resistor terminal" tovdeterminea fixed percentage of the total resistance of said resistor, a common voltage source for the other grids of said tetrodes, a common voltage source forthe anode-cathode circuits of said, tetrodes, 'means for increasingthe grid voltage to the striking point of the second'tetrode, and means'fonholding said striking point voltage of the second tetrode the initial unit voltage, and, a conductor connected to said element and? power unit adapted to without appreciable change until the first grid voltage on the first tetrode changes to the striking point voltage to cause current flow through said first tetrode,

3. A comparator as described in claim 2 in which the means for increasing the second grid voltage of the second tube to the striking point and holding it at said point until the first grid voltage of the first tetrodedrops to the striking point voltage, comprises a voltage divider connected across the second grid voltage source of the second tube, a capacitor andresistor connected in parallel between the negative terminal of the second grid voltage source and apoint on said divider, a vacuum tube connected between said voltage divider point and the cathodes of said tetrodes, the grid of said vacuum tube having connection to the negative terminal of said second grid potential source, a resistor connecting the positive terminal of the second grid potential source and said tetrod'ecathodes, and switch means opening the circuit ofthe resistor in parallel with said capacitor when the second tetrode strikes.

4'. In an electric control system, an electrical power unit: subject to voltage change-from an initial main voltage, a conductor connected to the power unit, anda percentage apparatus connected to said power unit, said percentage apparatus comprising a variable voltageelement, means applicable to said element for setting the percentage value of the main voltage at which the conductor is, energized, means for fixing the percentage setting means at the predetermined value, and additional means for energizing said. conductor ata change of main voltage to said'set percentage value.

5. In a. circuit subject to voltage change: and varying initial; voltage values for each application, of the load, in combination, a percentage apparatus for selecting a predetermined voltage percentage value of the initial voltage as applied toisaid circuit, said percentage apparatus. including, a gas electron tube having a cathode, an

anode, a first grid, and a second grid, meansresponsive to a component of circuit voltage. for applying, a voltage on the first grid in accordance with, the selected percentage of the initial voltage, means, for establishing a voltage-between the anode and cathode of said tube, automatic means, including an energy source and a deviceiorincreasing the flow of energy from said source, effective only after application of the initial voltage to said circuit for raising asecond gridvoltage until the tube reaches the striking point, automaticmeans, including mean-sfor halting the increase of, flow of energy from said energy source,v for fixing the secon grid voltage at the striking point whereby a reference voltage for control purposesis provided by the continued firing. of'said tube, and means conjointly responsive to. changed circuit voltage and the fixed'percentage voltage values fixed on and by" said tube for providing a signal impulse.

6'. In a circuit, subject to voltage change and varying initial voltage values for each application of the load, in combination, a percentage-ap paratus for selectively establishing-a predetermined percentage; voltage value ofan initialcircuit voltage, said percentage apparatus including a gas electron tube having a cathode, an anod'ea first grid; and a secondgrid, means responsive to acomponent of circuit voltage for applying a voltage on the first grid at, a: selected percentage ofthe initial circuit voltage, means for establishing a voltage between the anode and cathode of said tube, automatic means effective only after the application of the initial voltage to said circuit for increasing the second grid voltage to the striking point and for fixing the second grid voltage at the striking point of said tube, said second grid voltage raising and fixing means including a capacitor connected to said grid, means for charging the capacitor, means for discharging said capacitor to thereby cause the striking of said tube, means for preventing further discharge of the capacitor after the striking of said tube, and means conjointly responsive to changed circuit voltage and the fixed percentage voltage values fixed on and by said tube for providing a signal impulse.

7. In an electrical control system, a percentage apparatus for establishing a fixed percentage value of an initial voltage in a main circuit which comprises percentage means for selecting a percentage value of said initial voltage, and means for fixing said percentage value irrespective of changes in said main circuit voltage from the initial value, said fixing means including a capacitor connected to said percentage means, a power source for charging said capacitor to a predetermined voltage for initiating action of said fixing means, and additional means connected to said capacitor for maintenance of the capacitor voltage at the set voltage corresponding to said selected percentage voltage value.

8. In an electrical control system, a power element for inclusion in a power circuit, a control circuit subject to intermittent voltage changes, a conductor, and control means for producing intermittent energization of the conductor in synchronism with said control circuit voltage changes, said control means being operable only at the same percentage value of initial voltage and independently of the absolute initial value of the intermittent control circuit voltages and the resistance of said circuit.

9. In an electrical control system, a variable voltage control load, a control element connected to said load and variable in voltage therewith, a percentage means for selecting a percentage voltage of said element, means for fixing said percentage voltage automatically for any initial control element voltage, and an output device connected to said control element adapted for energization only on a change of voltage of the control load to a value forming a predetermined voltage ratio to the percentage voltage whereby an auxiliary power device is operated.

10. In an electrical control system, a control load subject to voltage change, a percentage means connected to said load for selecting a percentage voltage of said load, a conductor, means for fixing said selected percentage voltage automatically for any initial control load voltage, and means connected to said percentage means actuated only on a change of voltage of the control load to the selected and fixed percentage value for energizing the conductor.

11. In an electrical control system, in com-' bination, a control load subject to voltage change for each application of the load, a percentage means connected to said load for selecting a percentage of said load voltage, means for fixing said percentage voltage automatically and uniformly for any initial control load voltage in a sequence of intermittently applied load voltages, a normally non-conducting first thermionic tube connected to said percentage means, a conductor connected to said first tube, said percentage voltage fixing means comprising a second thermionic tube having a grid control means, a circuit including a source of power for said second tube, a circuit including a third thermionic tube connected to the grid means of the second tube, a capacitor connected to a grid of the third tube, means for charging the capacitor, means for discharging the capacitor and reducing the negative bias on the third tube grid whereby the positive bias on the grid means of the second tube is increased to a required conducting value, means for holding the capacitor at the charge point at which the second tube conducts, means for imparting a first bias to said first tube when the second tube conducts current, and means for altering the bias on said first tube to cause it to function to impart a signal impulse to said conductor when the load voltage becomes equal to the percentage voltage.

12. In an electrical control system, a variable voltage control load, a control element connected to said load and variable in voltage therewith, a percentage means for selecting a percentage voltage of said element, means for fixing said percentage voltage automatically for any initial control element voltage, and control means variable in voltage with said control load voltage for actuating power mechanism on a change of control load voltage to that of the selected percentage voltage.

13. A method of controlling supply of power from a power source to a series of welds in which the electrical resistance prior to weld fusion varies from weld to weld, which comprises experimentally determining for the workpiece the percentage change of resistance between weld electrodes occurring for a weld of the desired weld strength, successively applying the electrodes to the workpiece at the various weld points, supplying power to the electrodes at each successive weld point until the resistance at the weld changes to the predetermined percentage, fixing a current supply value determined as a percentage relative to that which it has at initial resistance at the weld, and utilizing the current change corresponding to said resistance percentage change at each weld to open the power supply thereto.

14. In a control system for interrupting supply of power from a power source to a welding load, a control element connected to said load and variable in voltage therewith, circuit means for fixing automatically a percentage voltage of the initial control element voltage for each intermittent power supply, and control means connected to said element and source for interrupting power supply to the load on equation of the control element and fixed percentage voltages.

15. In a control system for controlling supply of intermittent power to a welding load, a control element connected to said load and variable in voltage therewith, a percentage device for selecting a percentage voltage of said element, means for fixing said percentage voltage automatically for any initial control element voltage, and control means connected to said element and source for interrupting supply of power to the load on equation of the control element and fixed percentage voltages.

16. In a system of power supply control, a power source, a load subject to voltage change adapted to receive power from said source, and control means dependent on load resistance change for actuating a power device, said control means comprising a percentage device connected to said load for establishing a reference voltage at a fixed percentage of the initial load voltage, and power means connected to the percentage device and power device and operative at a selected fixed ratio between the load and reference voltages for actuating said power device.

17. In an electrical control system for resistance welding, a load subject to resistance change during applications of electric divider connected across said load in parallel therewith and subject to load voltage variation, percentage means connected to said divider for fixing a predetermined percentage value of the initial divider voltage as a reference voltage, and means actuated by a change of load voltage to a predetermined ratio to the reference voltage for controlling the supply of current to said load.

18. An electric control system for electric power units subject to voltage change, characterized by use of a voltage device connected across the power unit and variable in voltage therewith, percentage means connected to the voltage device for establishing as a standard, a voltage at a fixed percentage of the initial unit voltage, control means connected to the voltage device and percentage means subject to the voltage variation of said voltage device, and a translating device connected to said control means, said translating device being energized by said control means on voltage change of the voltage device to a predetermined value in relation to the standard voltage of said percentage means.

19. In an electrical control system, a load subject to changes from initial to secondary resistance values during supply of power thereto, energy response mechanism, and control means interposed between said load and energy response mechanism for energizing said mechanism on a change of load resistance from said initial value to a predetermined percentage value only of said initial value, said control means comprising an impedance connected to said load and subject to a voltage variablewith said load voltage, a percentage means for selecting and power, a voltage fixing a percentage value of said impedance voltage, a power actuator, and control means for energizing said actuator on change of impedance voltage to said fixed percentage value only.

20. In an electric control system for an electric resistance welder, in combination, an electric power source, a load unit including welding electrodes receiving electric current from said source and having a relatively sudden and pro nounced voltage change for each period of current application, a first grid tube, means for selectively fixing a charge through said tube in accordance with pre-change grid tube responsive conjointly to said fixed charge and a charge which, is determined by post-change voltage, and means for providing a control impulse for the welding control circuit when the post-change charge bears a predetermined relationship to the pro-change charge.

21. An electric welder control system as set forth in claim 20, further characterized by the fact that means are provided for pro-selecting the percentage relationship at which said control impulse is furnished.

22., An electric welder control system as set forth in claim 20 further characterized by the fact that said first tube is a gas tube which holds the charge at the fixed value.

RICHARD STILLMAN DAVIES.

REFERENCES CITED The following references are of record in the file of this patent:

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